Examples of electronically-controlled unit injectors for an engine are shown in U.S. Pat. No. 3,689,205 issued to Links on Sep. 5, 1972 and U.S. Pat. No. 4,392,612 issued to Deckard et al. on Jul. 12, 1983. In Links the fuel pumping plunger of the unit injector is hydraulically actuated whereas in Deckard et al. the fuel pumping plunger is mechanically actuated. In both of these electronically-controlled unit injectors, a solenoid assembly is provided which moves a poppet valve that controls actuating fluid or fuel pressure in the unit injector in order to control fuel injection delivery.
In the above electronically-controlled unit injectors, the motion of an armature of the solenoid assembly is hydraulically damped in order to help prevent the poppet valve from rebounding after it has contacted a seat or stop. In Deckard et al., the armature has a plurality of passages which extend through the armature for the passage of fuel during movement of the armature toward the opposed working face of an associated pole piece or stator. In Links, a channel is provided external to the armature which communicates with a pair of chambers located adjacent opposite end portions of the armature.
However, after the engine is stopped, an excessive amount of such damping fluid might remain in the solenoid assembly. This remaining fluid may then become more viscous as the engine cools off. Such viscous fluid may then cause slow response of the solenoid assembly and poppet valve during cold engine starting. Slow response of the solenoid assembly and poppet valve diminishes the fuel injection delivery capability and injection timing accuracy of the unit injector. The end result is that too much damping fluid in the solenoid assembly may hinder quick starting and/or operation of the engine, particularly under cold engine conditions.
The present invention is directed to overcoming one or more of the problems as set forth above.